Articular cartilage lesions are commonly occurring. In a prospective study of 1,000 knee arthroscopies focal chondral or osteochondral defects were found in 19% of the patients (Hjelle 2002). Chronic articular cartilage defects do not heal spontaneously. However, acute traumatic osteochondral lesions or surgically inflicted lesions extending into subchondral bone, e.g. by drilling (Pridie 1959), spongialization, abrasion or microfracture with an angled awl (Rodrigo 1994) causing the release of pluripotent mesenchymal stem cells from the bone marrow, may heal with repair tissue consisting of fibrous tissue, fibrocartilage or hyaline-like cartilage. The microfracture technique causes little damage to the subchondral bone plate and the risk of heat necroses caused by drilling or abrasion is eliminated. The quality of the repair tissue after these bone marrow stimulating techniques depends on various factors including the species and age of the individual, the size and localization of the defect, the surgical technique, e.g., how the subchondral bone plate is treated, and the postoperative rehabilitation protocol. Microfracture has been used in small traumatic defects in young sporting individuals (Steadman 2003) as well as in larger osteoarthritic lesions in older patients (Miller 2004, Steadman 2007). The purpose of the present study was to investigate the long-term clinical outcome 10 to 14 years after microfracture of articular cartilage defects in the knee and possible predictors of good and poor outcomes.